linux-kernel - Re: [PATCH 2/2] tpm/tpm_ftpm_tee: use send

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Message-ID: <Z-RlbEN9BoKnTN2E@kernel.org>
Date: Wed, 26 Mar 2025 22:37:09 +0200
From: Jarkko Sakkinen <jarkko@...nel.org>
To: Jason Gunthorpe <jgg@...pe.ca>
Cc: Sumit Garg <sumit.garg@...nel.org>,
	Stefano Garzarella <sgarzare@...hat.com>,
	linux-kernel@...r.kernel.org, Peter Huewe <peterhuewe@....de>,
	linux-integrity@...r.kernel.org,
	James Bottomley <James.Bottomley@...senpartnership.com>,
	Jens Wiklander <jens.wiklander@...aro.org>
Subject: Re: [PATCH 2/2] tpm/tpm_ftpm_tee: use send_recv() op

On Wed, Mar 26, 2025 at 05:58:33PM +0200, Jarkko Sakkinen wrote:
> On Wed, Mar 26, 2025 at 04:57:47PM +0200, Jarkko Sakkinen wrote:
> > On Wed, Mar 26, 2025 at 11:34:01AM -0300, Jason Gunthorpe wrote:
> > > On Wed, Mar 26, 2025 at 02:11:12PM +0200, Jarkko Sakkinen wrote:
> > > 
> > > > Generally speaking I don't see enough value in complicating
> > > > callback interface. It's better to handle complications in
> > > > the leaves (i.e. dictatorship of majority ;-) ).
> > > 
> > > That is very much not the way most driver subsystems view the
> > > world. We want to pull logical things into the core code and remove
> > > them from drivers to make the drivers simpler and more robust.
> > > 
> > > The amount of really dumb driver boiler plate that this series
> > > obviously removes is exactly the sort of stuff we should be fixing by
> > > improving the core code.
> > > 
> > > The callback interface was never really sanely designed, it was just
> > > built around the idea of pulling the timout processing into the core
> > > code for TIS hardware. It should be revised to properly match these
> > > new HW types that don't have this kind of timeout mechanism.
> > 
> > Both TIS and CRB, which are TCG standards and they span to many
> > different types of drivers and busses. I don't have the figures but
> > probably they cover vast majority of the hardware.
> > 
> > We are talking about 39 lines of reduced complexity at the cost
> > of complicating branching at the top level. I doubt that there
> > is either any throughput or latency issues.
> > 
> > What is measurable benefit? The rationale is way way too abstract
> > for me to cope, sorry.
> 
> E.g., here's how you can get rid of extra cruft in tpm_ftpm_tee w/o
> any new callbacks.

Measurable benefit: no need to allocate memory buffer.

Let's take that as a starting point ;-)

On that basis I can consider this (i.e. something to measure).

BR, Jarkko